Many construction and earth moving machines use hydraulic or pneumatic cylinders to move a work tool such as a bucket on a backhoe, a loader, or an excavator. The cylinder may include a cylinder rod coupled at one end to the work tool with a cylinder body having a chamber formed therein at the other end. Hydraulic fluid may be introduced into the chamber to extend the rod from the body and may also be removed from the chamber to retract the rod. Often, the rod position or the amount of the extension of the rod must be known so that movement of the work tool can be controlled or monitored.
Barcodes have been marked on cylinder rods in order to locate the position of the rod. In particular, the rod may be marked with a barcode including non-repeating segments of code, each of which correspond to a different location of the rod. In operation, a sensor is provided in the cylinder adjacent the barcode to identify a particular segment which is then associated with a corresponding rod location.
In some systems, the barcode is formed on the cylinder rod using a laser system. In these systems, the laser may heat a designated portion of the cylinder rod to anneal the surface, changing the color of the rod, thereby forming the lines of the barcode. However, such annealing may melt and redeposit a certain amount of material. In some instances, the laser energy is sufficient to remove the material through ablation, or alternatively, create plasmas capable of removing material. This results in an added surface roughness of the cylinder rod in the form of peaks and valleys, perpendicular to the direction the laser travels when marking. This added roughness may wear other materials that travel along the marked surface, such as sealing materials. Further, to get a good contrasting mark, it is often necessary to repeatedly expose the rod surface to the laser, thereby compounding the formation of peaks and valleys.
One system for forming a barcode on a surface is disclosed in U.S. Pat. No. 5,023,437 to Speicher. The '437 patent discloses creation of a barcode on a surface using individual imprinted marks to form a plurality of substantially linear rectangular arrays. The arrays are formed of a plurality of laser marks disposed adjacent each other in aligned rows and columns. However, spaces between the laser marks may be interpreted by a scanning reader to be empty bars of the barcode.
The present invention is directed to overcoming one or more of the problems in the prior art.